The present invention relates to a method for producing a flexible polyurethane foam using a polyol having a high molecular weight and a low hydroxyl value, and a flexible polyurethane foam thereby obtained.
Heretofore, a flexible polyurethane foam has been produced by using a polyol and by employing a production method of an open system such as a slab foaming method or a production method of a closed system employing a closed mold. The slab foam produced by the production method of an open system is produced usually by using a polyol having a molecular weight of from about 3,000 to 5,000, as the raw material polyol.
Usually, the polyol to be used as the raw material for a flexible polyurethane foam is produced by ring opening addition polymerization of an alkylene oxide such as propylene oxide using a polyhydric alcohol or the like as an initiator by means of a sodium type catalyst such as sodium hydroxide or a potassium type catalyst such as potassium hydroxide. By such a production method, a monool having an unsaturated bond (an unsaturated monool) will be formed as a by-product, and the amount of such an unsaturated monool to be formed, will increase as the hydroxyl value of the polyol decreases (as the molecular weight increases). If a flexible polyurethane foam is produced by using a polyol having a high unsaturation value, there will be a problem such as a decrease in hardness, a deterioration of the compression set or a decrease in curing during the molding. Further, if it is attempted to produce a polyol having a low hydroxyl value by means of a sodium type catalyst or a potassium type catalyst, the unsaturation value tends to be remarkably high, and the production tends to be very difficult. On the other hand, as a method for producing a polyol having a low hydroxyl value and a low unsaturation value, a method is known wherein an alkylene oxide is subjected to ring opening addition polymerization by means of a double metal cyanide complex catalyst.
If a double metal cyanide complex catalyst is used for the production, it is possible to produce a polyol having a low unsaturation value, but if a polyol having a high molecular weight such as one having a hydroxyl value of at most 15 mgKOH/g, is used as a raw material, the stability during the production of a foam tends to be low, and it has been considered difficult to produce a flexible polyurethane foam.
In order to overcome the above problem of moldability, a method has been proposed to produce a flexible polyurethane foam by using a polyol mixture comprising a polyol produced by means of a double metal cyanide complex catalyst and a polyol produced by means of a sodium hydroxide catalyst or a potassium hydroxide catalyst (JP-A-8-231676). However, such a proposal is concerned with a mold foamings, and no production examples is disclosed in which a high molecular weight polyol is employed. Here, in this invention, a word xe2x80x9cmoldabilityxe2x80x9d means, foam stability on producing of a polyurethane flexible foam by a slab foaming method. Thus, when a moldability is good, it means that there is no occurring of collapse or shrinkage.
Further, a method is also proposed to produce a slab foam by using a polyol having a hydroxyl value of from 10 to 80 mgKOH/g produced by means of a double metal cyanide complex catalyst (U.S. Pat. Nos. 6,028,230 and 6,066,683). However. Examples in these references disclose only cases wherein flexible foams are produced by a polyol having a molecular weight of 5,000, and no Examples are given in which higher molecular weight polyols are used.
Further, a method is also proposed to produce a flexible polyurethane foam excellent in mechanical properties such as tensile strength and elongation by using a polyoxyalkylene diol having an average molecular weight of at least 1,500 and a polyoxyalkylene diol having an average molecular weight of from 150 to 350, as essential components (JP-A-2-286707). In this publication, an example is disclosed in which if the above two components are not included, particularly if a polyoxyalkylene diol having two functional groups is not used, the mechanical properties tend to be inadequate. Further, in that publication, there is no disclosure with respect to an example for producing a flexible polyurethane foam using a polyol having a molecular weight of at least 5,000.
The present invention proposes a method for producing a flexible polyurethane foam wherein a polyol having a high molecular weight and a low hydroxyl value is used as a raw material, whereby it has been considered difficult to produce a foam. Further, the present invention provides a flexible polyurethane foam excellent in mechanical properties by using a polyol having a high molecular weight.
The present invention is an invention relating to a method for producing a flexible foam having good moldability, by using, as a raw material, a high molecular weight polyol having a low hydroxyl value. By using a high molecular weight polyol as the raw material, the obtainable flexible polyurethane foam has a characteristic that the mechanical properties are good. Further, the flexible polyurethane foam obtainable by the present invention has a characteristic that the change in the physical properties by a temperature change is little. Further, by using a double metal cyanide complex catalyst, it is possible to produce a polyol having a low unsaturation value and a narrow molecular weight distribution. As compared with a polyol having a wide molecular weight distribution, the polyol having a narrow molecular weight distribution has a low viscosity, whereby the foam stability at the time of producing the flexible polyurethane foam will be improved.
Namely, the present invention provides a method for producing a flexible polyurethane foam in an open state, which comprises reacting a polyol with a polyisocyanate compound in the presence of a catalyst, a blowing agent and a foam stabilizer, wherein as the polyol, a polyol having a hydroxyl value of at most 15 mgKOH/g is used.
Further, the present invention provides a flexible polyurethane foam produced by the above production method.